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Old 17th September 2012, 06:55 AM   #21
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Location: Colorado Springs, CO
Quote:
Originally Posted by j.michael droke View Post
Hi there SpM: Just ran a SPL check on an experimental OB (18" curved to 16.25") Uncalibrated generator, DVM and SPL meters: 2.83v:
130hz-70db, 140hz-65.8db, 150-58db, 160hz-71.4db, 170hz-75.3db, 180hz-76db,
190hz-78db, 200hz-78.8,300hz-84db, 400hz-8.3db, 500hz-85.2, 1k-84.4db, 1.5k-97.5db
2k-91db, 3k-97.2db, 4k-97.3db, 5k-97.4, 6k-97.5db, 7k-82.2db, 8k-87.5db, 9k-87.5db,
9k-87.5db, 9.3k85.1, 10k-62.8db. Since I intend to cross over to the bass unit around 150hz, I did not record the fall off below 130hz. ...regards, Michael
thanks.

What drivers did it have and what distance did you measure from?
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Old 17th September 2012, 09:13 AM   #22
AndrewT is offline AndrewT  Scotland
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Response difference from 160Hz to 4kHz is ~26dB.
Is that close enough to be worth trying to EQ that error out of the system?
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Old 17th September 2012, 05:51 PM   #23
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I'd like to get back to SpinMonster, who seems like a pretty sensible person.

The learned posts are helpful up to a point in the design process. But they are very little help in anticipating final results. Especially hard to anticipate are sounds in a room and even more, bass sound. And at the far end of the design process is measurement of results which adds a further complexity to the process with OBs.

Mid-range OB produce wonderful sound and likely half the secret of ESL delight. The learned discussions have little to do with making nice mid-range sound since neither the baffle nor the driver resonance need to be limitations. What's left is just canny choice of driver.

In the woofing department, nobody has emphasized the essential design element: you make use of the driver resonance to "build" your output compass - by choosing the right driver for your purposes. You don't fret about low freq roll-off, you try to cook it into the design in light of OB size.

Ben
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Dennesen ESL tweets, Dayton-Wright ESL (110-3200Hz), mixed-bass Klipschorn (28-110), and giant OB using 1960's Stephens woofer (18-110); Behringer DSP. HiFi aspirations since 1956
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Old 18th September 2012, 06:55 AM   #24
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Quote:
Originally Posted by bentoronto View Post
I'd like to get back to SpinMonster, who seems like a pretty sensible person.

The learned posts are helpful up to a point in the design process. But they are very little help in anticipating final results. Especially hard to anticipate are sounds in a room and even more, bass sound. And at the far end of the design process is measurement of results which adds a further complexity to the process with OBs.

Mid-range OB produce wonderful sound and likely half the secret of ESL delight. The learned discussions have little to do with making nice mid-range sound since neither the baffle nor the driver resonance need to be limitations. What's left is just canny choice of driver.

In the woofing department, nobody has emphasized the essential design element: you make use of the driver resonance to "build" your output compass - by choosing the right driver for your purposes. You don't fret about low freq roll-off, you try to cook it into the design in light of OB size.

Ben
I agree and as such I am nearly done with the test baffles which have a lower section with 1.55 cubes for bass under 200-300 should I have to go hybrid. I'm trying to see how my 21ft x 21ft x 9ft room will deal with reflections of other items such as huge subs.

Its a home theater with a 16 foot screen so the front wall cant get any treatment. This isnt the best picture but it shows what I'm dealing with. The first picture shows the placement of a currnt monopole at 4ft from the side walls, 5 feet from the front wall and 10 feet from the listening position. They are 52"tall. The subs are 2ft x 2ft x 52"
Click the image to open in full size.
Click the image to open in full size.

I figure I can move the seating back a few feet to get more clearance from the reflection off the sub boxes and maintain at least 4 feet or about an 8ms delay from the rear wave. A few measurements and go from there. I'm not interested in SPL as this is just a test system for reflections and imaging. I can then build something huge for SPL if it gives a real central image that I had with my apogees. That midrange was magic. Thanks for the input.

Last edited by SpinMonster; 18th September 2012 at 06:59 AM.
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Old 18th September 2012, 07:11 AM   #25
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One other thing, this isnt a full OB build as I have no intention of altering the low bass. I would go with a partial hybrid of having a sealed woofer in the test baffles to 200 or 300 and dipole from there up. I built the test baffles to allow for 2 7"midbass with one operating from 80 to 1.9K and the lower from 80 to about 500. If this doesnt get me any decent FR, I will then add a sealed box woofer to the base of the test baffles which is a sealed box which would move the cross to the 7's up a bit for power and more adjustment of FR. Im trying to stay with drivers I already own with the exception of the Neo 3PDRW's that I had to buy.

The reflected sounds make measuring a curiosity as it will differ near field to far field.

I will start a new thread to show where I am with the build and drivers. I just need to upload all the pics from the build.

I love this hobby.
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